Fun with tail recursion

(define sum (lambda (xs) (sum_h xs 0)))
(define sum_h (lambda (xs x) (cond
    ((equal? xs '())
        x
    )
    (#t
        (sum_h (cdr xs) (+ x (car xs)))
    )
    )
))

(define range (lambda (n m) (range_h n m '())))
(define range_h (lambda (n m xs) (cond
    ((>= n m)
        xs
    )
    (#t
        (range_h  n  (- m 1) (cons m xs))
    )
    )
))

(define rangestep (lambda (n m x) (rangestep_h n m x '())))
(define rangestep_h (lambda (n m x xs) (cond
    ((>= n (+ m 1))
        xs
    )
    (#t
        (rangestep_h (+ n x) m x (append xs (list n)))
    )
    )
))
(display  (range 0 10))